A heatwave warning has been issued as health workers and local authorities prepare for soaring temperatures.

Today Sussex was expected to hit 33C or 91F, hotter than Los Angeles and Ibiza.

The heat is set to continue for most of the week, leaving vulnerable people exposed to the dangers of the sun.

The NHS has drawn up guidelines to avoid sunstroke, sunburn and overheating.

Brighton and Hove City Council, West Sussex County Council and East Sussex County Council yesterday issued a major heatwave alert after the Met Office stepped up its emergency status to level three for the first time since the system was introduced in 2004.

Staff in children's and adults' services were advised of the risks.

Lionel Barnard, West Sussex Cabinet member for public protection, said: "We have taken this action because we want vulnerable people in our care to enjoy the sunshine while remaining safe.

"We're saying to all of our residents, yes the sunshine is a delight, but don't forget too much exposure to it can make you unwell."

A Brighton and Hove City Council spokesman said those most at risk were people aged 75 and over or under four, people taking certain types of medicine, those with mental health problems, dementia and people who are bed-bound or suffering from chronic disease.

Children have been warned to wear sun hats and sun cream and drink plenty of fluids.

Phil Smith, headteacher of Carlton Hill Primary School, Sussex Street, Brighton said: "We are on the case daily."

Lesley Corbett, headteacher at Carden Primary School, County Oak Avenue, Brighton, said: "We have special arrangements at lunchtime so the children are getting some fresh air but they are not spending a whole hour in the sun."

Brighton's Royal Sussex County Hospital had a 42 per cent rise in emergency cases on Sunday. While most patients had other conditions, some were suffering from heat-related illnesses.

Janet Cheesman, associate director for emergency services, said: "The trust would like to remind people to take every precaution to ensure they stay well."

Brighton and Hove City NHS Teaching Primary Care Trust also issued a warning.

Tom Scanlon, director of public health, said: "Many of us enjoy sunny weather but several hot days in a row can cause problems. During the warm weather we are advising people to keep out of the heat if they can, take cool showers or baths and drink water regularly."

Advice issued tells people to:

Avoid going out in the hottest part of the day (11am-3pm).

Wear sunscreen and a hat when outdoors.

Drink plenty of water.

Avoid alcohol.

Avoid strenuous activity in the hottest parts of the day.

Stay in the coolest rooms and shut curtains to keep out the sun.

Open windows on the first floor or above.

Drink regularly but avoid tea and coffee.

Seek medical advice if you have any concerns.

If you have symptoms of heat exhaustion, such as headaches, dizziness, nausea and vomiting, muscle weakness or cramps, pale skin and a high temperature, move somewhere cool and drink plenty of water or fruit juice. Take a lukewarm shower or sponge yourself with cold water.

If left untreated, heat stroke can develop. Symptoms are headaches, nausea, intense thirst, sleepiness, hot, red and dry skin, a sudden rise in temperature, confusion, aggression, convulsions and loss of consciousness.

Southern Water said during the weekend, 135-137 million litres of water were used in Sussex a day, up from 128 million litres during June. The company pointed out that without drought restrictions, it would expect customers to use 140 million litres.

Sales of ice cream went up by 118 per cent at Brighton's Asda supermarkets at the marina and Hollingbury industrial estate. Beer sold an extra 62 per cent and soft drinks sales increased by 20 per cent.